Filtered-OFDM系统频偏估计算法的研究

发布时间：2018-06-13 01:34

本文选题：F-OFDM + OFDM　；参考：《西南交通大学》2017年硕士论文

【摘要】：随着IMT-2020(5G)推进组对未来通信需求的明确,多种应用场景和业务需求给物理层波形的设计带来了新的挑战。2015年,华为在正交频分复用(OFDM)技术的基础上提出了基于子带滤波的正交频分复用(Filtered-OFDM,F-OFDM)技术,其通过子带滤波降低频谱带外泄露,各子带根据具体的业务需求灵活配置波形参数,从而实现了灵活自适应的空口技术。F-OFDM作为一种新兴的多载波技术,对频偏造成的载波间干扰(Inter-Carrier Interference,ICI)较为敏感。因此,有必要在当前F-OFDM研究现状的基础上,利用OFDM频偏估计算法来实现F-OFDM系统的频偏估计,以降低频偏对系统性能的影响。首先,本文系统地分析了无线信道的小尺度衰落特性以及频偏对OFDM系统的影响,并深入研究了现有的OFDM频偏估计算法,从理论推导和MATLAB仿真两个方面对不同算法的估计性能进行了验证分析。其次,根据不同子带的F-OFDM符号能够在时域共存而在频域分离,对子带资源分配和子载波映射进行了研究,并通过MATLAB仿真比较了不同子载波间隔和不同带宽对子带性能的影响,结果表明子载波间隔越大,多普勒频移对子带性能的影响越小。另外,验证了滤波操作能够有效地降低子带频谱带外泄露,从而使不同子带设置极低的保护间隔就能很好的抑制相邻子带间的干扰。最后,结合OFDM频偏估计算法与F-OFDM的系统特性,分析比较了 CP相关性算法、改进的CP算法、Moose算法和Classen算法在不同子带的估计精度。通过仿真分析可得:当子带的子载波间隔较大时,多普勒频移对子带性能的影响较小,且每个F-OFDM符号中插入的CP采样点较多,因此,子载波间隔较大的子带适合利用基于CP的频偏估计算法。当子带的子载波间隔较小时,多普勒频移对子带性能影响较大,并且子带的符号长度较长以及插入的导频序列较多,因此,子载波间隔较小的子带适合利用估计精度较高的数据辅助频偏估计算法。此外,在系统带宽与采样率保持一致的前提下,仿真比较了双子带F-OFDM系统与OFDM系统利用同一算法进行频偏补偿后的误码率。由于子带能够灵活设置波形参数以及频偏算法无法彻底消除频偏引起的ICI,使得F-OFDM系统的误码率要低于子载波间隔较小的OFDM系统的误码率,高于子载波间隔较大的OFDM系统的误码率,体现了 F-OFDM系统通过灵活配置波形参数能够有效的降低无线信道对系统性能的影响。
[Abstract]:With the IMT-2020 5G) propulsion team defining future communications requirements, multiple application scenarios and business requirements pose new challenges to the design of physical layer waveforms. Based on orthogonal Frequency Division Multiplexing (OFDM) technology, Huawei proposes a sub-band filter based orthogonal Frequency Division Multiplexing (OFDM) technique, which can reduce the leakage of spectrum out of band by subband filter, and configure waveform parameters flexibly according to specific business requirements. As a new multi-carrier technology, F-OFDM is sensitive to Inter-Carrier interference (ICI) caused by frequency offset. Therefore, it is necessary to use OFDM frequency offset estimation algorithm to realize the frequency offset estimation of F-OFDM system on the basis of the current research status of F-OFDM, so as to reduce the influence of frequency offset on the performance of F-OFDM system. Firstly, the small scale fading characteristics of wireless channel and the influence of frequency offset on OFDM system are systematically analyzed, and the existing OFDM frequency offset estimation algorithms are deeply studied. The estimation performance of different algorithms is verified and analyzed in terms of theoretical derivation and MATLAB simulation. Secondly, according to the F-OFDM symbols of different subbands can coexist in time domain and separate in frequency domain, the sub-band resource allocation and sub-carrier mapping are studied, and the effects of different sub-carrier spacing and different bandwidth on sub-band performance are compared by MATLAB simulation. The results show that the larger the subcarrier spacing, the smaller the influence of Doppler shift on subband performance. In addition, it is proved that the filtering operation can effectively reduce the out-of-band leakage of the sub-band spectrum, so that the interference between adjacent sub-bands can be suppressed very well by setting very low protection interval of different sub-bands. Finally, combining the characteristics of OFDM frequency offset estimation algorithm and F-OFDM system, the estimation accuracy of CP correlation algorithm, improved CP algorithm moose algorithm and Classen algorithm in different sub-bands are analyzed and compared. The simulation results show that the Doppler frequency shift has little effect on the performance of the sub-band when the sub-carrier spacing of the sub-band is large, and there are more CP sampling points inserted in each F-OFDM symbol. The frequency offset estimation algorithm based on CP is suitable for subbands with large subcarrier spacing. When the subcarrier spacing of the subband is small, the Doppler frequency shift has a great influence on the performance of the subband, and the symbol length of the sub-band is longer and the pilot sequence is more inserted. The subbands with small subcarrier spacing are suitable to use the data-aided frequency offset estimation algorithm with higher estimation accuracy. In addition, on the premise that the system bandwidth is consistent with the sampling rate, the bit error rate (BER) of the dual-subband F-OFDM system is compared with that of the OFDM system using the same frequency offset compensation algorithm. Because the subband can set the waveform parameters flexibly and the frequency offset algorithm can not completely eliminate the ICI caused by the frequency offset, the bit error rate of the F-OFDM system is lower than that of the OFDM system with small sub-carrier spacing. The BER of OFDM system is higher than that of OFDM system with large sub-carrier spacing, which shows that F-OFDM system can effectively reduce the influence of wireless channel on system performance by configuring waveform parameters flexibly.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.53

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